After putting Firmware-X.Y.Z on the iPod, when you first reboot your iPod it will update the contents of its flash ROM. Follow the instructions on your iPod's screen (to insert the charger) and DO NOT interrupt this process. If you interrupt it, then there is a very good chance that your iPod will be unusable.

FOR 5.5G USERSFor 5.5th GenerationiPod users: using mkfs.vfat often seems to work, but it creates FAT filesystems that the rockbox code doesn't always handle properly, resulting in non-booting ipods

The 5.5G5.5thGeneration iPod actually has a normal 512-byte sectors disk for the 3030GBGB model and a 1024-byte sectors disk for the 8080GBGB model. The 2048-byte sectors mentioned above is the sector size reported by the USB interface. Since it is exported as 2048-byte sectors, if we format the partition with 512-byte sectors the OF might be able to access it just fine but Linux would not be able to mount the filesystem.